Bearing device

ABSTRACT

Bearing device of magnet type for instruments and the like and non-contact support of one part relatively to another part by means of magnet fields wherein the one part is rotatable relatively to the other at least a part of a full turn. The novelty lies therein that the magnet devices intended to keep the rotatable part essentially centered relatively to the stationary part are off-set so that besides radially acting force components also axial force components biasing the rotatable part in an axial direction appear; and in that a connection device connecting the rotatable part with the stationary part and permitting the former to turn at least a portion of a turn is arranged along the axis of rotation so as to keep the rotatable part correctly off-set positioned.

TECHNICAL FIELD OF THE INVENTION

This invention relates to bearing devices with extremely low frictionfor the use for instance in Theological measuring devices and othersensitive instruments.

BACKGROUND OF THE INVENTION

In a known measuring instrument a movable instrument part is suspendedby means of and between vertical tapes or strings with low torsionresistance and having low starting torque. The movable instrument partis to be influenced by the power, the effect or the like to be measured.The moving coil galvanometer is one example of such an instrument.Instrument parts suspended by tapes or strings may be used forinstruments where the displaceable or rotatable part is influenced orbiased without physical contact, i.e. without mechanical influence fromanother part. For purposes where the object to be tested or otherwiseanalysed is to be physically attached to the movable part or where anindicating device or the like is to be mechanically connected to atransmitter the known arrangements are hardly usable.

It has been suggested to use—for bearings where low friction and lowstarting torque is required—different types of magnetic bearings. DE 3437 937 discloses a such device and more in detail a device for guidingand supporting rheological measuring systems. The intention was to bringabout, in a simple way, a guiding and supporting arrangement withminimum friction and based on one stationary and one mobile magnetsystem with a soft iron part arranged with a vertical air gap.

Already in the 19th century however it was proved by a Mr. EARNSHAW thata devices like the one according to the DE publication is functionallyimpossible because of their inherent instability. It is physicallyimpossible to achieve stability both axially and radially as ismaintained in the DE publication. The device according to the DEpublication not only has inferior lateral stability but is also unstablewhich means that it will collapse and loose its position either at theupper or the lower pair of magnets immediately.

To further clarify the state of the art and to define the invention overthe state of the art, it must be mentioned that the invention is basedprimarily on passive magnet systems including permanent magnets only.Active magnet bearings include electromagnets shaped and arranged in away very similar with the arrangement of a stator of a synchronousmotor, whereas the armature or rotor normally is formed by a circularpackage of transformer sheet metal. The position of the rotor is readand checked by means of a number of distance sensors the signals fromwhich via a quick acting boost control system optimises and distributessignals to each of the amplifier each controlling an electromagnet. Inthis way the rotor and shaft can be easily re-set and guided to itsintended position. Annular magnet bearings, often called passive magnetbearings include annular shaped permanent magnets which attractalternatively repel each other in such a way that stability is achievedin one desired direction only, radially or axially. In the otherdirection, however, the bearing will always be unstable, a fact whichwas proven more than a hundred years ago. If ever utilized, this type ofbearings always is used together with an auxiliary bearing such as anactive magneto bearing.

ASPECTS ON THE INVENTION

One purpose with the invention is to bring about, by utilising a passivemagnet system having a minimum of frictional resistance, an axially andradially stable bearing device especially but not exclusively forinstruments of rheometer type.

SUMMARY OF THE INVENTION

The invention is a bearing device for passively supporting one partmovable relatively to another part by means of magnets, preferablypermanent magnets in order to bring about a stable essentially frictionfree measuring of a torque in a range where conventional bearing systemsof the instrument ball bearing type or the like have too high a frictionand too high a starting torque and the characterising features of theinvention lies in that at one part and at another part, the one partrotatable relatively to the other part at least part of a revolution,pairs of magnet units arranged in a repulsion or attraction state arepositioned regarding their fields of force in such a way that forcecomponents hold the rotatable part in a predetermined radial positionand bias the rotatable part in an axial direction and in that at leastone mechanical, essentially stable positioning means is connectedbetween the one part and the other part and acting along the axis ofrotation for counterbalancing the force biasing the one part in the oneaxial direction.

BRIEF DESCRIPTION OF DRAWINGS

In the following the invention will be described more in detail withreferences to the attached drawing, in which,

FIG. 1 is a schematically axial section showing one embodiment of thebearing device with passive magnet bearings utilised for a viscosimeterof Couette type,

FIG. 2 is a schematically axial section of an embodiment with a passivemagnet bearing device utilised for an oscillating viscosimeter,

FIG. 2b is a schematically axial section through an embodiment with apassive magnet bearing device arranged with axially magnetisedconcentric magnets for a viscosimeter having including a cup,

FIG. 2c in an axial section shows an oscillating viscosimeter with onlya cup and an embodiment of a passive magnet bearing arranged withradially magnetised concentric magnets,

FIG. 3 shows in an axial cross section a viscosimeter of Couette typewith repulsive magnet bearings with passive magnets arranged in aparallel state,

FIG. 4 in a same way illustrates an oscillating viscosimeter with anattractive passive magnet bearing with the magnets arranged in parallel,and

FIG. 5 schematically shows ten different configurations withcombinations of radially and axially magnetised magnetos acting as aradial magneto bearing,

FIG. 6 schematically partly in cross section shows a Theologicalinstrument with a bearing according to the invention, and

FIG. 7 is a longitudinal sectional view of a further embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As an example of field of use has been selected viscosimeter especiallysuch ones for rheometer purposes and the viscosimeter is in the drawingssymbolised by a vessel marked K. The viscosimeter are very schematicallyillustrated and the purpose is to establish that a measuring is to takeplace with a medium inside the vessel K enclosing and surrounding acentral measuring body M. The bearing device naturally can be used forother types of instruments with rotational movements less than a fullcircle.

In all the embodiments shown, there is at least one pair of magnet unitsincluding one stationary magnet unit 1 and at least one movable magnetunit 2 and the magnet units are concentrically arranged relatively to anaxis around which one instrument part is rotatable. The shown magnetsunits have all permanent magnets, but it is theoretically possible toreplace the magnets of the one pair with electromagnets. Normallyseveral pairs of magnet units cooperate with each other.

The stationary magnet units 1 are arranged or affixed at a stationarypart, such as a support or stand 3 only schematically shown, whereas themovable magnet units 2 are arranged at or affixed to a rotatable part,such as a body or spindle rotatable relatively to the support or stand3. The two parts are connected by means of a connector 5 permittingrelative rotation over at least part of a revolution and the purpose ofthis will be further discussed below.

The pairs of magnet units 1 and 2 and their fields of force are soarranged relatively to each other that by means of the interaction theone or rotatable part 4 is kept centred relatively to the other orstationary part 3. This can be reached by means of repulsion ofattraction. On arranging any pair of magnet units to interact thereexists between the interacting fields of force—in a defined relativeposition—a so called null point, i.e. a relative position where a sortof equilibrium prevails. This equilibrium, however, is extremelyunstable and even a tiny mechanical disturbance causes the interactionto collapse resulting in an displacement of the relative positions ofthe parts involved.

According to this invention the interacting magnet units with theirfields of force are positioned relatively to each other off-set from thenull point, meaning that there appear, besides the essentially radialforce components working for mutually repulsing or attracting the parts,i.e. keeping the rotatable part centred relatively to the stationerypart, also axial force components which bias the rotatable part in theone axial direction or the other, depending on in which directionrelatively to the off-set point the parts are displaced. By arrangingbetween the one or rotatable part 4 and the other or stationary part 3the connector means 5 the axial biasing force is counterbalanced and theposition of the rotatable part, both radially and axially relatively tothe stationary part remains stable.

The connector means shown in FIGS. 1-4 is a so called torsion means,viz. a string or tape which allows rotation over at least part of arevolution and normally several revolutions with a minimum resistance.

It is also possible to use, in stead of the torsion means, string ortape taking up a tensional force, a connector means including lowfriction material co-operating with a pin or seat, i.e. a watch typebearing including pieces of hard materials such as diamond, ruby,sintered carbide or steel and co-operating pin or seat devices ofappropriate material. In this case the connection is subject to apressure instead of a tension as with the torsional means.

In the embodiment shown in FIG. 1 the viscosimeter is of Couette typeand includes a the vessel K supported by a motor shaft and the measuringbody M is to be dipped into the liquid inside the vessel. The measuringbody M is rigidly connected to the spindle 4. The magnets of thisembodiment are concentrically arranged and axially magnetised.Consequently the co-operation between the magnets or rather therepulsion forces try to push the spindle downwardly causing a tension inthe torsion string 5. The string however prevents any axial displacementof the spindle 4 and the result is that a balance is reached and thespindle is held exactly in the centre of the device.

The embodiment according to FIG. 2 differs from the one according toFIG. 1 in that there is no motor for rotating the vessel K, butotherwise the interaction between the magnets and the string is equalwith that of FIG. 1.

FIG. 2b shows another embodiment, and in this the magnets are arrangedin a way similar to that of FIGS. 1 and 2 but the support and spindlearrangement is inverted. Consequently the magnets of the support and ofthe spindle act in the opposite direction and strive for lifting thespindle out of the support. The torsion string 5 prevents any axialmovement upwardly of the spindle and the cooperating magnets of thesupport and the spindle create a stabilising force.

FIG. 2c differs form the just described embodiment in that the magnetsare radially magnetised. The magnets 1 of the support are directedmagnetically in a direction opposite to that of the magnets 2 of thespindle 4. The magnets 1 and 2 of FIG. 2c try to repel each other but asthe support does not give way outwardly and the spindle does not giveway inwardly the combined forces result in a position of equilibrium,which per se is unstable, but as the magnets 1 and 2 are mutuallyaxially offset there appear an axial force component trying to axiallydisplacing the spindle 4 relatively to and out of the support 3. Thislifting force is counteracted by the unyielding torsion string 5 and theresult is that the spindle is kept stable in the centre of the supportin a position defined both radially and axially.

In FIG. 3 is illustrated an embodiment utilised at a viscosimeter ofCouette type, i.e. similar with the viscosimeter according to FIG. 1,but the magnets 1′ of the support 3′ and the magnets 2′ of the spindle4′ are arranged in an axial arrangement. The magnets 1′ and 2′ areaxially displaced and otherwise so oriented that the magnet poles are ina repulsion state. The stationary magnets 1′ try to push the spindlewith the movable magnets 2′ out of the support 3′ but this iscounteracted by the string 5′ connecting the spindle 4′ to the support3′ thereby keeping the spindle in an axially defined position as well asin a radially well defined position.

The embodiment according to FIG. 4 illustrates a viscosimeter comparablewith the one according to FIG. 2 but as in the embodiment according toFIG. 3 the magnets are arranged in an other way than in the embodimentaccording to FIG. 2. According to FIG. 4 the magnets 1″ and 2″ arearranged in parallel with each other and axially displaced. In this casehowever the poles of the magnets are arranged in a way opposite to thataccording to FIG. 3, namely so that the stationary magnets 1″ try toattract the movable magnets 2″ and so to say try to pull the spindle 4″out of the support 3″. As in the other examples the torsion string 5″counteracts the axial displacing of the spindle.

The examples given in FIGS. 1 to 4 are the once now preferred especiallyfor instruments of the type shown.

FIG. 5 schematically shows no less than ten different configurationswith combinations of radially and axially magnetised magnets for radialpassive magnet bearing devices, which can be used for the bearing deviceaccording to this invention. In FIG. 5 no connecting means are shown asthe positioning of said devices depends on the selected off-setdirection and the type of connecting device chosen.

Item one is a combination with axially magnetised magnets and it isclearly visible that the inner and outer magnets are mutually offset inaxial direction.

Item two is combination of axially and radially magnetised magnets.

Item three is a combination of opposing axially magnetised magnets wherethe movable magnets are axially displaced relatively to the stationaryones.

Item four is an other example of magnets magnetised similar with theones of item two but where the movable magnets are placed beyond thestationary ones.

Item five is an arrangement similar to the one according to FIG. 4 thatis with attractive arrangement of the magnets.

Item six shows an arrangement with oppositely directed radiallymagnetised magnets.

Item seven shows the opposite to item two that is the movable magnetsare axially magnetised whereas the stationary ones are axiallymagnetised.

Item eight is an example where the movable and the stationary magnetsare magnetised unidirectional.

Item nine is comparable with item seven but the movable magnets aremagnetised in opposite directions and positioned beyond the stationaryones.

Item ten is comparable with item six but in this case the stationary andthe movable magnets are acting in different axial planes.

The embodiment according to FIG. 6 includes a support or stand 13 inwhich a vertical bore 7 is arranged. Around the bore 7 there arestationary magnets 11 and inside the bore 7 a spindle device 14 carryinga number of magnets 12 co-operating with the stationary magnets 11 ofthe stand 13. The spindle 14 is provided with a central bore 8 and hasat its upper end projecting above the stand a connection 9 for a torsionstring or wire 15 extending along the central bore of the spindle and soadapted that the spindle is kept in a defined axial position relativelyto the stand by the influence of the magnets 11 and 12, respectively, atthe stand and the spindle so that the resulting force strives to pushthe spindle upwardly, i.e. out of the bore of the stand. The torsionwire this way will determine the axial position and create a stabilisingforce holding the spindle in the centre of the stand bore 8.

At its upper end the spindle 14 has a conical head 10 adapted to bereceived in a complementary shaped recess R of a measuring vesselcarrier or holder.

The spindle 4 in the illustrated embodiment is provided with a drivingmeans D adapted to give the spindle a controlled limited rotationalmovement and a sensor means S also connected to the spindle andinfluencing a computer device for determining the properties of a liquidfilled into the vessel K.

As a torque resistance of the torsion string or wire 5 is known andconstant and also the force exerted by the driving means it is by meansof the sensing device in co-operation with the computer possible todetermine the properties of the liquid in the vessel.

The embodiments discussed above are generally intended for instrumentsand the like where the rotatable part rotates over a fraction of a turnor just a few turns. As mentioned above it is however possible toutilise a torsion means, a string or the like which allows a largenumber of rotations if this is required. If the device is intended for ause where the rotatable part is intended to rotate many turns, the axialpositioning against the axial thrust from the co-operating magnetos,normally is reached by means of an axial bearing e.g. of watch spindletype, where a pin is received in a recess in a piece of a hard materialsuch as diamond, ruby, sintered carbide or the like or of the type wherea spherical body attached to the one part is received in a partspherical seat at the opposite part. Such axial bearings, similar withthe torsion string or tape, naturally, are localised in such a way thatthe rotational axis thereof is congruent with the rotational axis of thebearings device as a whole. In the axial bearing types the bearing issubjected to an axial thrust or pressure, the contrary to the torsionmeans types where a tensional force acts along the torsion means.

The embodiment according to FIG. 7 shows one example of a device wherethere is no torsion means but instead a pin 5 x cooperating with abearing piece 6 x of saphire, ruby, diamond or the like hard material.The magnets are magnetised in such a way that the axial force componentthereof pushes the inner part 4 upwardly towards the bearing piece 6 x.The pin being rather weak has as only purpose to stabilize the innerpart 4 axially. From the same figure can also be seen a holed lid likelid like ond closure of the outer part 7 serving as an abutmentpreventing accidental axial movements of the inner part.

In the embodiments shown there are at least two pairs of magnet units,axially separated from each other. By arranging two sets of axiallyspaced magnet units as disclosed radial aligning or stability isachieved. If there was only one set of magnet units the rotatable partcould have a tendency to rock or swing, meaning that the axis ofrotation would deviate and rotate around the intended geometrical axis.By arranging two axially spaced magnet sets the axis of rotation isstabilized and kept aligned with the geometrical axis.

The magnet units in each set can be similarity oriented magnetically,i.e. so that they bias the rotatable part together in the samedirection. They can, however, also be oriented opposite to each other sothat they bias the rotatable part in opposite directions. In the laftercase, it is important that the biasing force of the one set of magnetunits overrides the biasing force of the other set of magnet units andthis is a necessity both in the case the units work inwardly againsteach other or outwardly from each other. In order to keep the rotatablepart in its intended position, there is, according to the invention,arranged a connector means which positions the rotatable part either bymeans of a torsion device or an pin bearing against a hard material orthe like.

In instruments where a rotatable part is supported by a connectorespecially by a torsion string balancing the axial force from the magnetunits, the rotatable part 3 could by accident be pushed inwardly so thatit not only reaches the null point but also passes this equilibriumposition. The result would be a total wrecking of the instrument. Inorder to reduce the risk for such accidents it is suggested to arrange asecond connector means acting in a direction opposite to the one of thefirst connector means and this means could be of torsion means type orhard material bearing type. The most convenient way is to attach oneconnector means at each axial end of the rotatable part but is in manycases more convenient to arrange at the one axial end only of arotatable part, a combined torsion string and hard material bearing bymounting the string inside a tube like device at either end having aseat or surface co-operating with a hard material piece. In this way theopposite end of the rotational part is free for attaching measuringvessels or the like.

To reduce the risk for, by mistake, pushing the rotatable part so thatit passes the null point and disappears into the stationary part, it isalso possible to arrange mechanical abutments either at the stationaryor the rotatable part or at both and design the abutments so that therotational part after a small axial displacement is prevented fromentering the stationary part alternatively to leave the stationary partif the connector means fails.

What is claimed is:
 1. A magnetic bearing device for use in instrumentsand which allows a rotational movement of a first part relative to asecond part and including at least one magnet unit at each of the parts,said magnet units creating magnetic fields, the forces of whichstabilize the parts relative to each other including in directionsradial to the axis of rotation of the first part, wherein the magnetunit or units (2) of the first, rotatable, part (4) is so localized andarranged relative to the magnet unit or units (1) of the second,stationary, part (3) that the interacting fields of force of the magnetunits (1,2) of the two parts create both radially acting stabilizingforce components and force components resulting in an axial displacementforce biasing the first, rotatable, part (4) in the one axial directionrelative to the second, stationary, part (3), and wherein at least oneaxially acting mechanical positioning means (5) is mounted to connectthe first part with the second part, said positioning meanscounteracting the axial force component biasing the first rotatable partand being at least in one direction axially stable, at least partiallyrotatable connector, wherein the connector is a torsion means (5)secured to the first rotational part at and extending along the rotationaxis thereof, said torsion means allowing at least limited rotation ineither rotational direction and preventing displacement in at least theone axial direction caused by the axial repelling force component.
 2. Abearing device according to claim 1, wherein the torsion means is atorsion wire.
 3. A bearing device according to claim 1, wherein thetorsion means is a torsion string.
 4. A bearing device according toclaim 1, wherein there are torsion means attached at each axial end ofthe first, rotatable, part and extend axially outwardly therefrom toappropriate securing points on the second, stationary, part, one of thetorsion means preventing axial displacement of the rotatable part in adirection opposite to the displacement preventing direction of the othertorsion means.
 5. A bearing device according to claim 1, whereinmechanical axial displacement preventing abutment portions are arrangedat at least one of the first and the second part, said portions uponengagement preventing the displacement of the rotatable first partrelative to the stationary second part beyond a minimum displacement. 6.A bearing device according to claim 1, wherein each magnet unit includesa number of axially magnetized magnets (2).
 7. A bearing deviceaccording to claim 6, wherein the magnets are concentrically arranged.8. A bearing device according to claim 1, wherein each magnet unitincludes a number of radially magnetized magnets.
 9. A bearing deviceaccording to claim 8, wherein the magnets are concentrically arranged.10. A bearing device according to claim 1, wherein the first part andthe second part (4, 3) are provided with axially in both directionsfacing abutment portions preventing axial displacement beyond a pre-setdistance in both axial directions.
 11. A bearing device according toclaim 1, wherein at least two axially spaced sets of magnets (2, 1) arearranged at the first, rotatable, part (4) as well as at the second,stationary, part (3), the magnetic force fields thereof being arrangedto give an excess of axial biasing force in the one direction, thisexcess force being counterbalanced by the mechanical positioning means(5).
 12. Analyses instrument comprising a bearing device according toclaim
 1. 13. A method for determining rheological properties of aliquid, comprising placing the liquid in a vessel (K) of an analysisinstrument according to claim 12 and recording and analyzing thereadings of the instrument.
 14. A method according to claim 13, theanalysis is performed by means of a computer program.